This invention relates to novel plastic compositions having enhanced environmental degradability.
The advent of plastics has given rise to improved methods of packaging goods. For example, polyethylene and polypropylene plastic films, bags, bottles, styrofoam cups and blister packages have the advantages of being chemically resistant, relatively unbreakable, light in weight and translucent or transparent. The increasing use of plastics in packaging applications has created a serious waste disposal problem. Burning of these plastic materials is unsatisfactory since it adds to air pollution problems.
Unlike some other packaging materials, such as paper and cardboard, plastics are not readily destroyed by the elements of nature. Thus, burying them is not an effective means of disposal, and can be expensive.
Plastics are biologically recent developments, and hence are not easily degradable by microorganisms which attack most other forms of organic matter and return them to the biological life cycle. It has been estimated that it may take millions of years for organisms to evolve which are capable of performing this function. In the meantime, plastic containers and packaging films are beginning to litter the countryside after being discarded by careless individuals.
Problems of litter and solid waste could be minimized if the rate of chemical deterioration of plastics could be enhanced. This would have the further advantage that the constituent atoms and/or stored energy in such plastics could be re-used in natural ecological processes.
The enhancement of the rate of environmental deterioration of plastics through the use of degradation-promoting additives is known in the prior art. For example, the preparation of degradable polyolefin films containing certain organic derivatives of transition metals is described in U.S. Pat. No. 3,454,510.
In most cases, the additives suggested for use as degradation-promoting agents are themselves non-polymeric in nature. The use of such additives can be complicated by their tendency to be removed from the polymer as a result of gradual vaporization, leaching, diffusion, and/or chemical destruction. Furthermore, the removal of additives under environmental conditions may lead to contamination of the air and water, hazards to wildlife, etc. Likewise, the use of such additives may detract from the useful physical properties of the plastics, and undesired degradation may occur during the preparation of polymer/additive mixtures and the fabrication of plastic articles therefrom.
The present invention is intended to avoid such difficulties through the use of polymeric degradation-promoting additives. A further objective is the minimization of solid-waste disposal problems through the development of secondary uses for recovered or off-grade plastics which are unsuitable for conventional uses.